Our invention relates generally to machine tools and more specifically to those equipped for the replacement of the cutting tools, when they are worn from use, with new ones. Still more specifically, our invention concerns a power driven machine for drilling small diameter holes in work such as, typically, printed circuit board (PCB) blanks (or insulating bases for PCBs), with particular emphasis on its facilities for the quick change of the worn drills.
PCB blank drilling machines have found widespread acceptance in the electronics industry for the mass production of PCBs of various circuit configurations. Generally, such machines comprise a plurality of drills releasably mounted to respected spindleheads above a table on which the work is to be mounted. The drills for use with PCB blanks are unique in the small diameters of their cutting bodies, being usually from about 0.1 to 1.5 millimeters. Such small diameter drills are of course susceptible to ready wear, especially at their lips or cutting edges. A quick replacement of the worn drills is one of the prerequisites for the higher production of the machine.
We are aware of several prior art drilling machines equipped for drill change. According to one such known machine, which we believe is most pertinent to our invention, a row of new drills are mounted upstandingly along one edge of the table. These new drills are engaged and held by the overhead spindles for use. When worn, the old drills are released from the spindles and deposited upstandingly on the table. Then another set of new drills which have been kept standing by on the table are caught by the spindles.
One of the problems with this known drill change system is that separate fluid actuated cylinders or like actuators are employed for the loading of successive new sets of drills on the table and for the withdrawal of the old sets of drills therefrom. The drill changers with the many actuators as well as means associated with each actuator have been bulky in size and complex in construction, adding substantially to the space requirements and manufacturing costs of the drilling machines themselves.
We also object to the prior art drilling machines with the tool changing capability in connection with the recovery of the worn drills. The common practice with PCB blank drilling machines is to regrind the used drills for reuse. Therefore, when the machine employs different diameter drills, they should be recovered separately, and in as neatly arranged form as possible, to expedite the subsequent process of redressing. Care must also be taken so that the drills may not be chipped or otherwise impaired through forced contact with one another or with other parts during recovery.